Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Summary of Long-term Debt

The following table summarizes the Company’s long-term debt.

	September 30,			December 31,
	2018			2017
3.875% Convertible Senior Notes, due March 15, 2019	$	89,990		$	89,990
4.25% Convertible Senior Notes, due March 1, 2037		143,750			143,750
3.95% Promissory note, due through February 17, 2020		9,185			9,360
4% Promissory note, due through February 1, 2031		7,981			8,348
3.75% Promissory note, due through September 1, 2036		8,372			8,613
4.55% Promissory note, due through August 1, 2036		5,982			—
Capital lease obligation, due through August 15, 2023		58			—
Total principal amount		265,318			260,061
Less: unamortized discount and issuance costs		(16,774	)		(22,226	)
Total long-term debt	$	248,544		$	237,835

Summary of Future Maturities of Long-Term Debt

The following table summarizes future maturities of long-term debt as of September 30, 2018, which takes into consideration the assumption that the 4.25% Convertible Senior Notes are repurchased at the earliest call date.

Due in 12 months following September 30,
2018	$	91,302
2019		10,058
2020		1,160
2021		144,958
2022		1,258
Thereafter		16,582
Total	$	265,318

Schedule of Interest Expense Related to Long-Term Debt

Information with respect to interest expense related to long-term debt is as follows:

	Three Months Ended					Nine Months Ended
	September 30,					September 30,
	2018			2017		2018			2017
Interest Expense:
Contractual interest	$	2,717		$	2,662	$	8,024		$	7,766
Non-cash expense (a)		1,888			1,746		5,556			4,623
Capitalized interest (b)		(53	)		—		(53	)		(61	)
	$	4,552		$	4,408	$	13,527		$	12,328

(a) Includes amortization of debt discount and issuance costs.

(b) Interest was capitalized for construction projects which are intended for lease.